1001 A+B Format (20 分)

1001 A+B Format (20 分)
Calculate a+b and output the sum in standard format – that is, the digits must be separated into groups of three by commas (unless there are less than four digits).

Input Specification:
Each input file contains one test case. Each case contains a pair of integers a and b where −10
6
≤a,b≤10
6
. The numbers are separated by a space.

Output Specification:
For each test case, you should output the sum of a and b in one line. The sum must be written in the standard format.

Sample Input:
-1000000 9
Sample Output:
-999,991

#include<iostream>
#include<string>
#include<stdlib.h>
#include<algorithm>
using namespace std;
int main() {
	long a, b;
	string c;
	cin >> a >> b;
	c = to_string(a + b);
	int len = c.length();
	for (int i = 0; i < len; i++) {
		cout << c[i];
		if (c[i] == '-') continue;
		if ((i + 1) % 3 == len % 3 && i != len - 1) cout << ",";
	}
	return 0;
}